Method and means for obtaining dry gas or air



1968 I. E. R. AKERMAN 3,395,511

METHOD AND MEANS FOR OBTAINING DRY GAS OR AIR 3 Sheets-Sheet 1 LJLILJUUFiled Sept. 25, 1964 Aug. 6,1968 E. R. AKERMAN I 5" Q METHOD AND MEANSFOR OBTAINING DRY OR AIR Filed Sept. 25, 1964" r a Sheets-Sheet 2 Fig.2

mvsmox. IWAN ERNST ROLAND AKERMAN ERIC Y. W NSON Aug. 1968 E. R. AKERMAN3,395,511

METHOD AND MEANS FOR OBTAINING DRY GAS OR AIR Filed Sept. 25, 1964 3Sheets-Sheet 3 LILILJLJLJ 24 Fig.3

INVENTOR. 1w? ERNST ROLAND AKERMAN BY ERIC Y. W

United States Patent 3,395,511 METHOD AND MEANS FOR OBTAINING DRY GAS 0RAIR Iwan Ernst Roland Alterman, Stockholm, Sweden, assignor to AtlasCopco Aktiebolag, Nacka, Sweden, a corporation of Sweden Filed Sept. 25,1964, Ser. No. 399,254 Claims priority, application Sweden, Oct. 3,1963, 10,791/63 2 Claims. (CI. 55-23) This invention relates to a methodand means for obtaining dry gas, such as dry air or the like. It is wellknown in connection with the production of dry gas such as dry air tocompress moist gas or air, to cool the compressed gas or air and tosubmit the gas or air to a first mechanical moisture separation, andafterwards to conduct the relatively dry gas or air through a moistureadsorber in which a second moisture separation is perfomed underpressure while the gas is fiowing in direction towards a place ofconsumption or a receptacle, and alternately with the above procedure toregenerate the moisture adsorber by means of previously dried gas or airwhich is conducted through the moisture adsorber at a pressure so muchlower that it is capable of carrying away a substantially largerquantity of moisture per kilogramme gas or air than the quantity carriedby the compressed gas or air entering the moisture adsorber from thecompressor. Means or apparatus applying the above method may be used fordrying gas, especially air, which may be used for supplying electricalcables with dry air under pressure or for other purposes. Such cablesmay, for instance, be telephone cables or other electrical cables intowhich compressed dry air is introduced in order to prevent moisture fromentering the cables, which might cause malfunction in their operation.The invention may also be used for producing dry air for compressed airnetworks in workshops, for paint spraying, for supplying dry air topneumatic instruments, and for many chemical and other processes and forother purposes where it is desirable to have available dry air or gashaving such a low moisture content that no condensation will occur evenat the lowest temperatures at which the network or the apparatusinvolved or in the process may operate.

Compressed air systems for supplying dry air to cable networks mustoperate continuously so that the cable net work is continuously suppliedwith a fresh amount of dry air which corresponds to the amount ofleakage from the network. In systems of the type above described aportion of the compressed gas or air is used for regenerating theadsorber by conducting dry gas or air with reduced pressure through theadsorber at suitable intervals. Said reduced gas or air is conductedthrough the adsorber preferably in opposite direction to the gas or airintended for the place of consumption in order to remove from theadsorber moisture collected therein. The quantity of dry air or gaswhich is necessary for regenerating the adsorber naturally involves anexpense which affects the economy of such a system as well as thecapital investment for compressors and other components of the system.It is consequently an object of the present invention to reduce thequantity of regenerating gas as much as possible. This may be achievedin different ways. One method according to the invention which hasseveral advantages comprises storing a part of the extremely drycompressed gas or air produced in the system in a receptacle andreducing a predetermined amount of such stored gas or air to such a lowpressure that said gas or air is capable of removing several times theamount of moisture which could be removed by the compressed gas or airentering the moisture adsorber from the compressor, said pressurereduced gas or air being conducted through the moisture adsorber3,395,511 Patented Aug. 6, 1968 to regenerate its moisture adsorbingability. The predetermined amount of low pressure gas is so calculatedthat it is just sutficient for regenerating the moisture adsorber thusavoiding excess dry gas or air from being conducted through the moistureadsorber for regenerating purposes and wasted. According to theinvention it is also important and advantageous to heat the quantity ofgas or air which is used for regeneration before it is introduced intothe moisture adsorber for regenerating pur poses. Such heating may becarried out by utilizing the compression heat from the compressorforming .a part of the system. Separate electrical heating means orother means of heating the regenerating gas or air may also be used. Formany practical purposes the pressure of the regenerating gas or air isreduced to about atmospheric pressure. However, in cases where pressurebelow atmospheric or vacuum is available the pressure of theregenerating gas or air may be reduced to subatmospheric pressure orvacuum which greatly increases the moisture carrying ability of theregenerating gas or air and thereby reduces the amount necessary forregeneration. The means for carrying out the method according to theinvention may take several forms. The predetermined amount of lowpressure gas or air may, for instance, be stored in a separatereceptacle or it may be released from a main receptacle for apredetermined length of time and through a flow restriction device so asto insure that the predetermined amount of gas or air is used only forregenerating purposes. The invention may also be employed in connectionwith apparatus working on a continuous principle.

In the accompanying drawings a number of embodiments of means accordingto the invention are illustrated by way of example. FIG. 1 is adiagrammatical view of a plant for producing dry air for supplying acable network in which plant extremely dry air for regenerating purposesis collected in a separate receptacle which serves also as aregenerative heat exchanger in which the air for regenerating theadsorber is collected. FIG. 2 is a diagrammatical view of a plant whichis a modification of the plant in FIG. 1 in which the extremely dry airin the auxiliary receptacle is electrically heated. FIG. 3 is adiagr-ammatic view of a plant in which two moisture adsorbers arearranged in parallel and in which each moisture adsorber is providedwith an auxiliary receptacle for storing the gas or air of predeterminedvolume which is to be used for regenerating purposes.

The plant illustrated in FIG. 1 consists of a compressor 1 which isdriven by a motor 2 which may be an electric motor. The compressor drawsair through an inlet conduit 31 and delivers compressed air to a network20 which comprises a regenerative heat exchanger 3 and a cooler 4 foraftercooling the air compressed in the compressor 1 as well as a waterseparator 5 of the mechanical type which may be emptied by opening anelectromagnetically operated valve 6 connected to the atmosphere througha drain pipe 18. In the separator 5 a first moisture separation of themain part of the water in the compressed air takes place. The relativelydry air flowing from tthe water separator 5 through a conduit 16 passesthrough a second separator which is a moisture adsorber 7 which maycomprise a vessel filled with silica gel or other suitable moistureadsorbing material or which may be carried out as a molecular filtercapable of retaining water and other undesirable constituents in thecompressed air. From the adsorber 7 a conduit 21 leads to a check valve8 and a network 22 which is connected to a pressure reducing valve 9 anda main receptacle 11 and through valve 9 to a compressed air network 23and a place of consumption 10 which may be a telephone cable network orother consumer. The compressor 1 may preferably be so dimensioned thatit delivers considerably more compressed air than the amount used by theconsumer 10. The valve 9 functions in such a way that it keeps thepressure constant in the compressed air network 23. The main receptacle11 is provided with a pressure responsive switch 12 which, when acertain pressure in the main receptacle 11 is attained interrupts thecurrent supply to the motor 2 and simultaneously actuates the elecromagnetic valve 6 so that said valve opens the drain conduit 18 fromthe mechanical moisture separator 5. Reference numeral 19 indicates theelectrical connection between the switch 12 and valve 6 and motor 2.Reference numeral 24 indicates a relief valve.

Between the moisture adsorber 7 and the check valve 8, a conduit 17 isbranched off through a flow restriction orifice 13 to an auxiliaryreceptacle 14. The orifice 13 permits the receptacle 14 to be loadedwith dry air during the loading period for the main receptacle 11. Saidauxiliary receptacle serves as a regenerative heat exchanger andcomprises suitable tube lobes 3 which together with a lobe 4 form theaftercooler of the compressor. Heat, which is delivered through thelobes 3 is stored by the compressed air and heat storing bodies 15 inthe auxiliary receptacle 14 and in the walls of the receptacle itself,which is provided with heat insulation 45. The receptacle 14, therefore,operates as a heat accumulator for gas or air of substantially the samepressure as that prevailing in the main receptacle 11. When thecompressor has stopped and the first moisture separator 5 is vented tothe atmosphere through the valve 6, then the pressure in the adsorber 7is reduced by Way of a pressure reducing means 13a which, in thisinstance, is a vacuum producing means. Subsequently, dry, warm,compressed air which has been stored in the auxiliary receptacle 14flows through the pipe 17, the restriction 13 in Which the pressure isreduced to a low value, for instance in the vicinity of atmosphericpressure, and through the adsorber 7 where the dry and still rather hotair due to its low pressure and elevated temperature is capable oftaking up the moisture which has been collected in the adsorber and tocarry away said moisture through the valve 6 and through the ventpassage 18 to the atmosphere. During this regeneration of the adsorber7, the check valve 8 is closed and the cable network is fed from the mandry air receptacle 11. When the pressure in said main receptacle hasdropped to a predetermined value, the pressure switch 12 18 again closedwhich results in the closing of the circuit to the electric motor 2 andthe starting of the compressor. Simultaneously the electromagnetic valve6 is moved to closed position so that venting of the moisture separator5 is interrupted. Then a new supply of dry compressed air is conductedto the consumer 10 and the main receptacle 11 through the moistureadsorber and the check valve 8 until the pressure switch againinterrupts the circuit to the motor 2.

In the modification illustrated in FIG. 2 the same reference numerals asin FIG. 1 have been used to indicate equivalent parts. Said parts aretherefore not described again. The plant according to FIG. 2 differsfrom the plant illustrated in FIG. 1 in that the heat accumulatmgauxiliary receptacle 14 is replaced by an auxiliary receptacle 14 inwhich the air is heated electrically. The plant is in other respectsarranged in the same manner as the plant in FIG. 1 with the exceptionthat the heat supply to the auxiliary air receptacle 14 is obtained froma source of current which delivers current to a heatin element 26 withinthe auxiliary air receptacle 14 for heating the air in said receptacle.Preferably said source of current 25 may be arranged to be connected assoon as the auxiliary receptacle 14 starts to deliver dry air forregenerating the moisture adsorber 7. When the pressure switch 12 stopsthe motor 2 and opens the valve 6, then dry hot air flows from theauxiliary receptacle 14 through the restric tion 13 and through themoisture adsorber 7 and carries moisture from said adsorber to theatmosphere.

The plant according to FIG. 3 is intended for use where continuousdelivery from a continuously running compressor is desired. This may bethe cause in connection with industrial plants, workshops, paintspraying plants or other places where a continuous demand of extremelydry air is present. The plant in FIG. 3 is provided with two moistureadsorbers 35, 36 arranged in parallel and each moisture adsorber isconnected to a conduit 43, 44, which through a flow restriction device39, 40 is branched to an auxiliary receptacle 41, 42 and which otherwisethrough check valves 37, 38 communicates with a conduit network 22leading to the consumer 10 and the main receptacle 11. The auxiliaryreceptacles 41, 42 may be unheated or they may be provided with meansfor direct or regenerative heating as indicated in connection with thedevices 14 in FIGS. 1-2 described hereinabove. A shift valve 33 isprovided in the conduit 16 leading from the first moisture separator 5to the adsorbers 35, 36 and said shift valve serves to alternatelyconnect the compressor to one of the moisture adsorbers 35 or 36,respectively, at a time while the other moisture adsorber is connectedto a vent conduit 34. The shift valve is moved periodically between theillustrated position and a position in which adsorber 35 is vented and36 is connected to the compressor delivery by a relay 46. Two checkvalves 37, 38 prevent air escape from the main receptacle 11 through themoisture adsorber which is under regeneration, 32 is a relief valve forprotection of the compressor against excess pressure. Otherwise theplant or apparatus according to FIG. 3 is similar to the apparatus inFIG. 1. It is obvious that during the time when one adsorber 35, 36 isoperative to collect moisture the other adsorber is regenerated by dryair from the pertaining auxiliary receptacle 41, 42, respectively, thearrangement being such that the necessary time for regeneration isalways shorter than the time of moisture adsorption.

The embodiments of the invention above described and illustrated on thedrawings should only be considered as examples and the invention may bemodified in several different ways within the scope of the followingclaims. It is for instance possible to provide more than two moistureadsorbers 35, 36 in parallel. Drain pipe 18 may be connected to acondenser or vacuum source.

What I claim is:

1. A method for obtaining extremely dry gas comprising; compressingmoist gas in a compressor wherein heat is produced, cooling thecompressed air, separating moisture mechanically from said compressedgas to produce relatively dry gas, conducting said relatively dry gasunder pressure through a moisture adsorber in which moisture isseparated from said relatively dry compressed gas to produce extremelydry gas for use by a consumer, conducting said extremely dry gas througha main line to a main receptacle, storing a part of said extremely drycompressed gas in said main receptacle, storing a predetermined amountof said compressed dry gas in an auxiliary receptacle branched off fromthe main line in continuous flow communication with said moistureadsorber through a flow restricting device, reducing the pressure ofsaid predetermined amount of such stored extremely dry compressed gas tosuch a low pressure that said gas is capable of carrying several timesthe amount of moisture which would be carried by the compressed gasentering the moisture adsorber from the compressor, supplying said heatproduced during compression of the gas in the compressor to saidpredetermined amount of dry gas by indirect heat exchange in saidauxiliary receptacle, and conducting said predetermined amount ofextremely dry low pressure and heated gas through said moisture adsorberto regenerate its moisture adsorbing ability.

2. Apparatus for obtaining extremely dry gas comprising a compressorprovided with an inlet conduit and a delivery conduit, cooling means insaid delivery conduit, a mechanical moisture separator in said deliveryconduit,

a moisture adsorption means in said delivery conduit after said coolingmeans and mechanical moisture separator, a check valve, means forconveying extremely dry gas from said adsorption means through saidcheck valve to a main receptacle and a consumer device communicatingwith said receptacle, an auxiliary receptacle for storing apredetermined amount of said compressed dry gas, means providing heatinsulation to said auxiliary receptacle, a conduit means for deliveringa portion of said extremely dry gas to said auxiliary receptaclebranched off from said conveying means before said check valve, meanscarrying said delivery conduit through said receptacle to delivercompression heat to said receptacle and the gas therein, means forinterrupting delivery from said compressor to the adsorption means,means for lowering the pressure in 15 the adsorption means, and meansfor conveying said predetermined amount of extremely dry gas from saidauxiliary receptacle through a pressure reduction device to and throughthe adsorption means in order to regenerate the adsorption means.

References (Iited UNITED STATES PATENTS 2,955,673 10/1960 Kennedy et al.55---33 X 3,141,748 7/1964 Hoke et a1. 5562 X 3,147,095 9/1964 Kanuch55-33 X 3,192,686 7/1965 Berkey et al. 5562 X 3,193,985 7/1965 Siggelin55180 X 3,205,638 9/1965 Hagle 5525 X SAMIH N. ZAHARNA, PrimaryExaminer.

J. ADEE, Assistant Examiner.

1. A METHOD FOR OBTAINING EXTREMELY DRY GAS COMPRISING; COMPRESSINGMOIST GAS IN A COMPRESSOR WHEREIN HEAT IS PRODUCED, COOLING THECOMPRESSED AIR, SEPARATING MOISTURE MECHANICALLY FROM SAID COMPRESSEDGAS TO PRODUCE RELATIVELY DRY GAS, CONDUCTING SAID RELATIVELY DRY GASUNDER PRESSURE THROUGH A MOISTURE ADSORBER IN WHICH MOISTURE ISSEPARATED FROM SAID RELATIVELY DRY COMPRESSED GAS TO PRODUCE EXTREMELYDRY GAS FOR USE BY A CONSUMER, CONDUCTING SAID EXTREMELY DRY GAS THROUGHA MAIN LINE TO A MAIN RECEPTACLE, STORING A PART OF SAID EXTREMELY DRYCOMPRESSED GAS IN SAID MAIN RECEPTACLE, STORING A PREDETERMINED AMOUNTOF SAID COMPRESSED DRY GAS IN AN AUXLIARY RECEPTACLE BRANCHED OFF FROMTHE MAIN LINE IN CONTINUOUS FLOW COMMUNICATION WITH SAID MOISTUREADSORBER THROUGH A FLOW RESTRICTING DEVICE, REDUCING THE PRESSURE OFSAID PREDETERMINED AMOUNT OF SUCH STORED EXTREMELY DRY COMPRESSED GAS TOSUCH A LOW PRESSURE THAT SAID GAS IS CAPABLE OF CARRYING SEVERAL TIMESTHE AMOUNT OF MOISTURE WHICH WOULD BE CARRIED BY THE COMPRESSED GASENTERING THE MOISTURE ADSORBER FROM THE COMPRESSOR, SUPPLYING SAID HEATPRODUCED DURING COMPRESSION OF THE GAS IN THE COMPRESSOR TO SAIDPREDETERMINED AMOUNT OF DRY GAS BY INDIRECT HEAT EXCHANGE IN SAIDAUXILIARY RECEPTACLE, AND CONDUCTING SAID PREDETERMINED AMOUNT OFEXTREMELY DRY LOW PRESSURE AND HEATED GAS THROUGH SAID MOISTURE ADSORBERTO REGENERATE ITS MOISTURE ADSORBING ABILITY.